The present invention is in the field of battery technology and, more particularly, electrolyte formulations that enable both low temperature and high temperature operation of lithium ion batteries.
Lithium ion batteries enjoy relatively widespread use, but to some extent their use is limited by the properties of existing lithium ion technology. For example, certain applications for lithium ion batteries require wide operating temperature ranges. For some applications, it is desired that lithium ion batteries operate at temperatures as low as −40 degrees Celsius and in other applications it is desired that lithium ion batteries operate at temperatures as high as 50 degrees Celsius. Indeed, some lithium ion batteries may need to be capable of operating across this wide temperature range.
At low temperatures, lithium ion batteries can exhibit a diminished power capability as compared to their power capability at room temperature. This diminished power capability may be explained by one or more factors, or a combination thereof. Namely, the power capability of lithium ion batteries is diminished at low temperature due to: (i) an increase in viscosity of the electrolyte resulting in slower lithium ion diffusion; (ii) a decrease in conductivity of the electrolyte; (iii) a decrease in conductivity of the solid electrolyte interphase (SEI) on the anode; and (iv) a decrease in the diffusion rate of lithium ions through the electrode materials, especially the anode.
Past attempts to address the problem of diminished power capability at low temperature generally consist of adding solvents with very low melting points to the electrolyte formulation. The intent behind adding such solvents is to keep the formulation from freezing or otherwise having reduced viscosity at low temperature. However, these solvents tend to be detrimental to high temperature cycle life.
Thus, there exists a need for an electrolyte formulation for a lithium ion battery that mitigates the decrease in power capability at low operating temperature yet has high temperature cycle life comparable to, or better than, conventional electrolytes.
These and other challenges can be addressed by certain embodiments of the invention described herein.